High-horsepower engines fueled with a gaseous fuel stored in a liquid state are employed in a variety of applications including locomotives, marine vessels, mining, mine haul trucks and power generation. Even though requirements can vary, common technical challenges exist across these applications. In this regard, fuel storage vessels are often large and difficult to co-locate with the engine due to the relatively large volume of fuel consumed. In locomotive applications in particular, the locomotive does not have sufficient space to locate a liquefied gaseous fuel storage vessel on board, which instead is located on an alternative railroad car near the locomotive.
Another challenge involves the thermal management of a heat exchanger employed to vaporize the liquefied gaseous fuel before introduction into the engine. Normally waste heat is the primary heat source for vaporizing the liquefied fuel which results in the best engine efficiency. On cold start the engine coolant temperature is low and there is a risk of freezing the vaporizer due to the relatively large flow rates. To mitigate this risk, it is advantageous to employ a secondary source of heat during at least engine cold start to prevent vaporizer freeze. Traditional sources of energy from the pre-existing engine could be used to generate this heat, but in many applications these energy sources are not able to supply the amount of energy required by the vaporizer.
Two development goals for high-horsepower engines fueled with liquefied gas are to have lower emissions than, and a power level similar to, an equivalent diesel engine. These engines would have wide adoption in the foregoing applications. The development of such engines has been attempted in the locomotive industry with little success. Another development goal is a high-horsepower engine that can be employed in the foregoing applications without any or very little modification or reconfiguration. High-horsepower applications comprise technical challenges which, although present in lower horsepower applications, are exacerbated at the higher power level. These challenges comprise, among others, ignition and combustion stability which are related in some manner to fuel pressure, and thermal management of the fuel supply.
Since the early 1980s several research projects and demonstration programs have attempted to employ natural gas as a fuel for locomotives. The initial motivation was to determine if a reduction in emission levels could be obtained compared to diesel locomotives, while maintaining the same level of power. These efforts were driven by evolving emission standards for locomotives from the Environment Protection Agency (EPA). In 1997 the EPA established Tier 0, 1 and 2 standards for locomotives, and more recently in 2008 they set the Tier 3 and 4 standards. Both the Tier 3 and 4 standards dramatically reduce emissions of diesel particulate matter (PM) and nitrogen oxide (NOx). Out of these efforts only one proven and tested commercially available natural gas fueled line-haul locomotive emerged, which employed a low pressure injection technology. In a paper titled “An Evaluation of Natural Gas-fueled Locomotives”, published in November 2007 by BNSF Railway Company, Union Pacific Railroad Company (UPRR), the Association of American Railroads, (together known as the Railroads) and the California Environmental Associates, the Railroads position on natural gas fueled locomotives was presented. Except for some potential niche applications, the Railroads expressed their belief that there was no viable opportunity to use natural gas as a locomotive fuel to help meet emissions and performance goals. This position was based on those research projects and demonstration programs and the one known commercially available natural gas fueled line-haul locomotive available in North America. This commercially available product was a conversion kit for the EMD 645 two-stroke diesel engine that enabled the locomotive to run on liquefied natural gas (LNG) as a primary fuel, while employing diesel as a pilot fuel. The LNG fuel is vaporized and injected at low pressure (85-125 pounds per square inch (psi)) such that the fuel and air mix during compression. A small portion of diesel “pilot” fuel is then injected into the cylinder at the top of the stroke where it auto-ignites to facilitate combustion.
Several of the research projects and demonstration programs attempted high pressure injection techniques where natural gas fuel was injected late in the compression cycle. In 1992 the UPRR began two of these efforts in separate programs with Electro Motive Diesel (EMD) and GE Transportation Systems (GE) to investigate the use of natural gas in line-haul, high-horsepower locomotive engines. This was a significant, multi-year effort in which UPRR expended over $15 million exploring basic engine and fueling technology issues. The natural gas injection pressures employed in both the EMD and GE systems were in the range between 3000 psi and 4500 psi. Due to technical limitations, the locomotives developed separately by EMD and GE were incapable of revenue operation. The technical difficulties in both programs included failure of gas injectors, failure of cryogenic LNG pumps for handling the cryogenic fuel between the tender tanks and the locomotives, the engine control system software, the gas transition control system software, and fuel system joint leaks.
The conversion kit for the EMD 645 (the commercially available product mentioned above) developed out of a project started by Burlington Northern Railroad (BN) in 1987 involving a two pronged effort to develop natural gas fueling infrastructure and line-haul locomotives capable of running on natural gas. For the fueling infrastructure, BN worked with Air Products and Chemicals (APC) to develop fueling locations and cryogenic tank-equipped tender cars to support the use of Refrigerated Liquid Methane (RLM), a high purity form of liquefied natural gas, as a locomotive fuel. In a paper titled “LNG as a Fuel for Railroads: Assessment of Technology Status and Economics”, published by the Gas Research Institute in January 1993, Bob Kirkland of APC indicates that LNG vaporization can be performed on the locomotive or on the tender car. “As less energy is needed to pump a liquid than to compress a gas, future tender car designs will likely deliver liquid to a pump located on the locomotive and upstream of the vaporizer. It would be impractical, according to Bob Kirkland, for the tender car to supply high pressure liquid to the locomotive. Such an arrangement would involve long lengths of high-pressure piping as well as additional hardware between the locomotive and the tender car to power the pump.”
Based on the admissions of the Railroads and the results of the research and demonstration projects cited above it is evident that late cycle, high pressure direct injection of natural gas in a locomotive engine is not a straightforward or obvious undertaking. Several technical challenges exist that have prevented a commercially available natural gas locomotive from emerging that can challenge and improve upon the emissions from so called clean diesel locomotive technologies. Similar challenges exist in employing natural gas as a fuel for internal combustion engines employed in marine applications for powering and propelling ships, in mining and mine haul trucks, and in power generation.
In light of the foregoing, there is a need for both a low pressure and high pressure fuel apparatus for high-horsepower engines that is adaptable for varying applications, and which solves technical challenges related to fuel pressure and thermal management. The present application provides an improved technique for supplying a gaseous fuel stored in a liquefied state to an internal combustion engine employed in a high-horsepower application.